How's your hydration? Yeah, I know, recent studies seem to indicate that cramping might not have anything to do with hydration ... and yet, when I'm dehydrated, I cramp. I'll cramp walking down the street after work if I haven't drunk much water during the day.
When I start to feel the warning signs of a cramp, or the beginnings of a cramp, I start to drink, and drink, and drink ... and it goes away. I also take electrolytes to balance the drinking.